Curable resin compositions and process for preparing oligomers containing acrylate groups and substituted methacrylate groups

ABSTRACT

A curable resin composition which exhibits excellent hardness of their curing products as well as storage stability is provided, and a simple method to obtain acrylated resins is provided. The composition comprises a curable oligomer which has an acryloyl group and a substituted methacrylate group represented by the following structure  
                 
 
     The process comprises a reaction step of reacting at least one monomeric multifunctional acrylate in the presence of a tertiary organic phosphine.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to curable compositions comprising solubleoligomers having acryloyl groups and substituted methacrylate groups,and a process for preparing said oligomers. These oligomers may beself-crosslinked by radiation or crosslinked in reactions with otherresins. The oligomers of this invention are useful as binders in curableinks and coatings.

[0003] 2. Description of Related Art

[0004] Resins having acryloyl groups are widely used in industry, as forexample as coating materials for paper, wood, metal and plastic, inprinting inks, adhesives and sealants. The hardening of the materialshaving acryloyl groups is achieved by polymerization of the acryloylgroups with electron beam or with the help of a radical initiator.Furthermore, acrylates are able to crosslink with other reactive resins,such as unsaturated polyesters, polyacetoacetates or polyamines. Thecommercial production of resins, containing acryloyl groups, isperformed by esterification of polyols with an excess of acrylic acid(Prepolymers and Reactive Diluents for UV- and EB-curable Formulations,P. K. T. Oldring (Ed.), SITA Technologies, London, UK, 1991, Page 124,131).

[0005] However, the curing composition containing said esterificationproducts containing acryloyl groups has a drawback which is lacking inhardness and in storage stability. Furthermore, though saidesterification is widely used, this process bears several drawbacks.Acrylic acid, for example is rather unstable at elevated reactiontemperatures and carries the risk of spontaneous uncontrolledpolymerization, if not properly inhibited. The high viscosity of theprepared acrylate resins is another problem, aggravating the eliminationof the excess of acrylic acid and the acidic catalyst after thereaction. Additional solvents are added to reduce the viscosity, so thatthe excess of acrylic acid as well as the acidic catalyst can be removedby repeated washing with alkaline aqueous solutions. The purification bydistillation, often used in the case of low molecular monomericacrylates, is not possible. The commercially used alternative method toobtain arcylated resins, the transesterification of polyols withmonomeric short chain alkyl acrylates, exhibits, besides the abovementioned purification problems, also the problem of the separation ofthe formed alkyl alcohols during the reaction. These alkyl alcohols mustbe removed to proceed the reaction without removing the alkyl acrylates,which is difficult due to the small difference in boiling points, sothat long and effective packed separation column are necessarilyrequired.

BRIEF SUMMARY OF THE INVENTION

[0006] It is therefore an object of the invention to provide a curableresin composition which exhibits excellent hardness of their curingproducts as well as storage stability, and to provide a simple method toobtain acrylated resins.

[0007] Inventors found that said problems were solved by using oligomershaving acryloyl groups which are produced by reacting di-, tri-, tetra-,penta- and hexacrylate monomers, which are commercially availablecommodity and are produced in high volume, in the presence of tertiaryorganic phosphines.

[0008] Accordingly, the present invention provides a curable resincomposition comprising a curable oligomer having an acryloyl group and asubstituted methacrylate group represented by the following structure.

[0009] Another object of the present invention is to provide a processfor preparing a curable oligomer which has an acryloyl group and asubstituted methacrylate group represented by the following structure,

[0010] comprising a reaction step of reacting at least one monomericmultifunctional acrylate in the presence of a tertiary organicphosphine.

DETAILED DESCRIPTION OF THE INVENTION

[0011] According to the present invention, curable resins are formed,which contain reactive acryloyl groups and reactive substitutedmethacrylate groups only by foregoing simple way. The curable resincompositions thereof are useful as UV-curable and thermosettingproducts.

[0012] The process of this invention is characterized in that thereaction of di-, tri-, tetra-, penta- and hexafunctional acrylatemonomers among each other in the presence of tertiary organicphosphines, does not give crosslinked, solid and insoluble products, butsoluble oligomer, having reactive acryloyl groups and reactivesubstituted methacrylate groups. It is amazing that the reaction ofespecially tri-, tetra- and higher functionalized monomeric acrylatesdoes not result in crosslinking as seen with a radical initiator such asperoxo- or azo-initiators.

[0013] As the formation of the oligomers containing acryloyl groups andsubstituted methacrylate groups (hereinafter abbreviated to “theoligomers of this invention”) is achieved by a simple mixing process,the preparation is simplified compared to the commercially appliedprocesses. No volatile splitting products are formed, no solvents areused and no further purification is required. Moreover, the scope of theproduct properties is wide as the process can be applied to anymonomeric compound, containing two or more acryloyl groups. As thereaction proceeds also at room-temperature, the risk of an uncontrolledpremature polymerization of the acryloyl groups is unlikely.

[0014] Monomeric di-, tri-, tetra-, penta-, and hexafunctionalacrylates, useful for the preparation of the oligomers of this inventionas starting materials are for example 1,4-butandiol diacrylate,1,6-hexandiol diacrylate, dipropylenglycol diacrylate, neopentylglycoldiacrylate, ethoxylated neopentylglycol diacrylate, propoxylatedneopentylglycol diacrylate, tripropylene glycol diacrylate, bisphenol-Adiacrylate, ethoxylated bisphenol-A diacrylate, poly(ethylene)glycoldiacrylate, trimethylolpropane triacrylate, ethoxylatedtrimethylolpropane triacrylate, propoxylated trimethylolpropanetriacrylate, propoxylated glycerol triacrylate,tris(2-hydroxyethyl)isocyanurate triacrylate, pentaerythritoltriacrylate, ethoxylated pentaerythritol triacrylate, pentaerythritoltetraacrylate, ethoxylated pentaerythritol tetraacrylate,ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate,dipentaerythritol hexaacrylate or mixture thereof.

[0015] Tertiary organic phosphines useful for the preparation of theoligomers of this invention as catalysts are for exampletriethylphosphine, tripropylphosphine, triisopropylphosphine,tributylphosphine, triisobutylphosphine, tri-tertiary-butylphosphine,tris(2,4,4-trimethylpentyl)phosphine, tricyclopentylphosphine,tricyclohexylphosphine, tri-n-octylphosphine (TOP),tri-n-dodecylphosphine, trivinylphosphine, tribenzylphosphine,dimethylphenylphosphine, cyclohexyldiphenylphosphine,dicyclohexylphenylphosphine, 1,2-bis(diphenylphosphino)ethane,1,3-bis(diphenylphosphino)propane, 1,4-bis(diphenylphosphino) butane,tertiary arylphosphines, activated by electon donating groups —OR or—NR₂ (R═H, C₁-C₁₂-alkyl, C₁-C₁₂-aryl) as for examplediphenyl(2-methoxphenyl)phosphine, tris(4-methoxyphenyl)phosphine,tris(2,6-dimethoxyphenyl)phosphine,tris(4-dimethylaminophenyl)phosphine, tertiary alkylphosphines,containing phosphorous bound hetero atoms as for examplehexamethylenetriaminophosphine and hexaethylenetriaminophosphine.Preferred among the above-exemplified tertiary organic phosphines aretiralkylphosphines having C5-10 alkyl groups in the scope ofanti-hydrolysis property of their products.

[0016] The oligomers of this invention are prepared by mixing themonomeric di-, tri-, tetra-, penta-, and hexafunctional acrylates andthe tertiary organic phosphines, then reacting them. The tertiaryorganic phosphines may be added all in once or in portions orcontinuously. After the addition a slight exothermic reaction isobserved. The amount of the added tertiary organic phosphines is withinthe range of 0.1 to 25% by weight, preferred 1.5 to 10% based on thetotal amount of the composition. The reaction is usually completed afterseveral minutes. The obtained products show viscosity in the range of200-100000 mPas at 25° C. and a number molecular weight (Mn) in therange of 300-15000. It is also possible to perform the reaction atelevated temperatures of 30-140° C. The products are colorless orslightly yellow. The viscosity and the molecular weight of the oligomersof this invention is controlled by the amount of catalyst and theacrylate functionality of the monomeric acrylate starting material. As arule, the higher the average acrylate functionality of the mixture andthe higher the amount of added phosphine catalyst, the higher theachieved molecular weight and viscosity.

[0017] In a preferred embodiment, the tertiary organic phosphines isadded in small portions, preferably drop by drop, so as to keep thetemperatures being within the range of 30 to 140° C., preferred 60 to90° C. Thus, higher molecular weights are obtained compared to themethod where the catalyst is added all at once at room-temperature.Therefore, if the producing process for an oligomer with a definedmolecular weight is desired, the addition of catalyst in small portionscan save the catalyst, thereby the addition leads to a cost advantageover the addition of the catalyst all in once.

[0018] Analytical methods revealed, that the oligomers of this inventionalso contain a certain amount of substituted methacrylate groups. Thehydrogen atoms of the substituted methacrylate groups have been provenin proton nuclear magnetic resonance spectroscopy at σ=6.2 and 5.6 ppmbesides the signals for the acrylate groups. The ¹³Carbon nuclearmagnetic resonance spectroscopy confirms the presence of substitutedmethacrylate groups of the following structure

[0019] The chemicals shifts of carbon atoms 1-8 of the structuredepicted above, measured from the product in example 1, are shown in thetable below: C-atom C¹ C² C³ C⁴ C⁵ C⁶ C⁷ C⁸ σ (ppm) 172 166 139 125 6160 33 27

[0020] The oligomers of this invention are formed by the reaction of twoacryloyl groups at a time, resulting in substituted methacrylate groupswhich link the acrylate monomers together. In this way, oligomers andlower polymers are created. Completely unforeseen was the observation,that the reaction of the acryloyl groups among each other proceeds onlypartially and leaves behind a stable resin having adequate acryloylgroups, which may be crosslinked later by light or heat. As the reactionis self-terminating within a short time period, a liquid solubleacrylated resin is created. The degree of oligomerization is controlledby the amount of the tertiary organic phosphines. The more tertiaryorganic phosphines is used as catalyst, the higher the obtainedmolecular weight and viscosity. The formed substituted methacrylategroups are polymerizable themselves as well and may also later increasethe glass transition temperature of the hardened product, sincemethacrylates show higher glass transition temperatures than acrylates.The oligomers of this invention are storage stable. Once the reactionfades away, there is no further increase in viscosity, even not atcelevated temperatures. Storage stability tests of the oligomers of thisinvention at 60° C. over two weeks did not show any stability problems.

[0021] The oligomers of this invention contain an adequate amount ofacrylic groups, which were not consumed during the oligomerizationprocess and which are now useful to enable crosslinking reactions,leading to cured products, as for example solvent resistant coatings.

[0022] The curable resin composition of the invention comprises theforegoing oligomers as essential components and does not always need aninitiator for their curing, because the oligomers have goodself-closslinking ability by electron beam or UV radiation. Even ifcured without any initiators, good harden products can be obtained,which may be used for solvent resistant coatings.

[0023] However, using initiators is more preferable for curing theoligomers. Namely the compositions of the invention further contain aninitiator. Of course, the oligomers are also able to react with othercompounds such as β-dicarbonyl compounds, amines or unsaturatedpolyesters.

[0024] As the initiator, there may be used any initiators such as a freeradical initiator for example peroxo-or azo-initiators or a photoinitiator.

[0025] A preferred curing method is the crosslinking by electron beam orUV radiation. In the latter method, photo initiators are dissolved inthe oligomers of this invention.

[0026] The amount of added photo initiators is within the range of 0.5to 12% by weight, preferred 2 to 7% by weight. Suitable photo initiatorsare selected from the group consisting of benzophenones, benzilketales,dialkoxy acetophenones, hydroxyalkylacetophenones, aminoalkylphenones,acylphosphinoxides and thioxanthones, for example benzophenone,methylbenzophenone, 4-phenylbenzophenone,4,4′-bis(dimethylamino)-benzophenone,4,4′-bis(diethylamino)-benzophenone, 2,2-dimethoxy-2-phenylacetophenone,dimethoxyacetophenone, diethoxyacetophenone,2-hydroxy-2-methyl-1-phenylpropan-1-one,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one,2-methyl-1-[4(methoxythio)-phenyl]-2-morpholinopropan-2-one,diphenylacylphenyl phosphinoxide, diphenyl(2,4,6-trimethylbenzoyl)phosphinoxide, 2,4,6-trimethylbenzoylethoxyphenyl phosphinoxide,2-isopropylthioxantone, 4-Isopropylthioxanthone,2,4-dimethylthioxanthone.

[0027] The above mentioned photo initiators are state of the art andcommercially available. The oligomers of this invention may be used asprepared or, if required, diluted with additional acrylate oligomersuntil the desired application viscosity is reached. The UV-curing of theoligomers of this invention in presence of photo initiators gives hardand colorless products, which are useful as coatings. The table showsthe composition of radiation curable mixtures, their viscosity, theamount of applied radiation for curing and the solvent resistance andhardness of the cured coatings. Radiation Solvent- Pencil- SystemComposition Viscosity² Intensity¹ resistance³ hardness⁴ 1 Product ofexample 1 96.0% 880 0.275 >75 DR 5H Irgacure184  4.0% mPas J/cm² 2Product of example 1 73.0% 280 0.275 >75 DR 4H TPGDA⁵ 22.0% mPas J/cm²Irgacure 184  5.0% 3 Product of example 1 30.0% 300 0.275 >75 DR 5HTPGDA 33.5% mPas J/cm² EPAC⁶ 30.0% Darocur1173  6.5% 4 Product ofexample 1 30.0% 290 0.275 >75 DR 4H TPGDA 33.5% mPas J/cm² EPAC 30.0%Darocur 1173  4.0% BzP⁸  2.5% MDEA⁷  1.5%

[0028] If desired, other resins or compounds having reactive groups,which are able to react with the acrylate groups and the substitutedmethacrylate groups in the the oligomers, can be incorporated in thecurable resin composition of the invention.

[0029] As the other resins or compound having reactive groups, there canbe mentioned, for example, unsaturated polyesters, or a compound havingactive hydrogen such as β-dicarbonyl compounds.

[0030] Another example for the use of the oligomers of this invention isthe curing with unsaturated polyesters. In this application, unsaturatedpolyesters can be incorporated in the curable resin compositions.

[0031] To prepare the composition containing the unsaturated polyester,the oligomers are mixed with the unsaturated polyester and an initiatormixture is added. In the present examples the initiator mixture containsa peroxide and a metal salt coinitiator. The following table gives twoexamples of the curing of the oligomers of this invention together withunsaturated polyesters. Solvent Pencil- System Compositon g resistancehardness 1 Polylite CN 610* 7.00 (unsaturated polyester, dissolved in40% styrene) Product of example 1 3.00 >75** 4H** 2-Butanone peroxide0.10 OctaSoligen Cobalt 6 0.05 2 Polylite CN 450* (unsaturated 6.00polyester, Dissolved in 2-hydroxyethylacrylate) Product of example 14.00 >75** 4H** 2-Butanone peroxide 0.10 OctaSoligen Cobalt 6 0.05

[0032] Another example for the application of the oligomers of thisinvention is the crosslinking in a Michael addition with compoundshaving active hydrogens such as β-dicarbonyls. In this application,compounds having active hydrogens can be incorporated in the curableresin compositions.

[0033] The curing proceeds in presence of a strong base such as1,8-diazabicyclo(5.4.0)undec-7-ene, 1,5-diazabicyclo(4.3.0)non-5-ene ortetramethyl guanidine. The following table gives two examples of thecuring of the oligomers of this invention together with acetoacetatesand malonates. Solvent Pencil- System Composition g resistance hardness1 Product of example 1 9.00 Bisacetoacetate, obtained from 1.00 methylacetoacetate >75 3H and 2-ethyl-2-butylpropandiol *DBU 0.20 2 Product ofexample 1 5.00 Polymalonate, obtained from 5.00 dimethylmalonate andethylene glycol >75 2-3H DBU 0.20

[0034] Objects and advantages of this invention are further illustratedby the following examples, but the particular materials and amountsthereof recited in these examples, as well as other conditions anddetails should not be construed to limit this invention.

EXAMPLES Example 1

[0035] 200.0 g of trimethylolpropane triacrylate was heated to 85° C.and sparged with air. 2.0 g of tri-n-octylphosphine was added and thereaction temperature increased to 103° C., indicating the start of thereaction. Then 3.8 g of tri-n-octylphosphine was added dropwise so thatthe temperature did not exceed 106° C. Then, the mixture was stirred foranother hour at 90° C. and was allowed to cool down to room temperature.The product exhibit a viscosity of 1300 mPas at 25° C. Molecular weightaverage Mw=1340.

Example 2

[0036] 550.0 g of ethoxylated trimethylolpropane triacrylate (TMPEOTA,Trademark of UCB) was heated to 80° C. and sparged with air. Then, 20.0g of tri-n-octylphosphine (TOP) was added in portions of 2.0 g inintervalls of 3 minutes. During this procedure the reaction temperatureincreased to 106° C. After the addition of the catalyst, the reactionmixture was stirred for another hour at 100-105° C. and was then allowedto cool down to room temperature. The product shows a viscosity of 2700mPas at 250° C. Molecular weight average Mw=3200, molecular numberaverage Mn=1200.

Example 3

[0037] 9.50 g of trimethylolpropane triacrylate (viscosity: 90 mPas at25° C.) was treated with 0.35 g of tri-n-octylphosphine (TOP) at roomtemperature. After the addition of the catalyst, the temperature raisedto 50° C. Then, the mixture was allowed to cool down to room temperatureyielding a colorless solution. Viscosity: 400 mPas at 25° C. Molecularweight average Mw=950, molecular number average Mn=670° C.

Example 4

[0038] To 9.50 g of trimethylolpropane triacrylate (viscosity: 90 mPasat 25° C.), 0.35 g of tri-n-octylphosphine (TOP) was added dropwise atroom temperature, whereas the temperature increased to 35° C. Then, themixture was allowed to cool down to room temperature yielding acolorless solution. Viscosity: 700 mPas at 25° C. Molecular weightaverage Mw=1130, molecular number average Mn=950° C.

Example 5

[0039] To 9.50 g of trimethylolpropane triacrylate (viscosity: 90 mPasat 25° C.), 0.35 g of tri-n-octylphosphine (TOP) was added dropwise at90° C. within a time period of 5 minutes. Then, the mixture was stirredfor another hour at 90° C. and was then allowed to cool down to roomtemperature yielding a slightly yellow colored solution. Viscosity: 1100mPas at 25° C. molecular weight average Mw=1430, Molecular numberaverage Mn=1060° C.

Example 6

[0040] To 9.50 g of trimethylolpropane triacrylate (viscosity: 90 mPasat 25° C.), 1.00 g of tri-n-octylphosphine (TOP) was added dropwiseunder vigorous stirring whereas the temperature increased toapproximately 60-70° C. The mixture was allowed to cool down to roomtemperature yielding a colorless solution. Viscosity: 23000 mPas at 25°C. Molecular weight average Mw=2560, molecular number average Mn=1290.

Example 7

[0041] To 9.00 g of trimethylolpropane triacrylate (viscosity: 90 mPasat 25° C.), 0.80 g of tri-n-dodecylphosphine was added dropwise undervigorous stirring whereas the temperature increased to 50° C. Themixture was allowed to cool down to room temperature yielding acolorless solution. Viscosity: 15000 mPas at 25° C. Molecular weightaverage Mw=2160, molecular number average Mn=1190.

Example 8

[0042] To 9.50 g of trimethylolpropane triacrylate (viscosity: 90 mPasat 25° C.), 0.50 g of tri-n-octylphosphine was added dropwise understirring within a period of 10 minutes, whereas the temperatureincreased to 50° C. Then, the mixture was stirred for another hour at90° C. before the mixture was allowed to cool down to room temperature,yielding a slightly yellow colored solution. Viscosity: 2500 mPas at 25°C. Molecular weight average Mw=1450, molecular number average Mn=1030.

Example 9

[0043] 100.0 g of trimethylolpropane triacrylate was warmed to 90° C.and sparged with air. Then, 3.0 g of tri-n-octylphosphine was added,whereas the temperature increased to 102° C. Then, another 7.0 g oftri-n-octylphosphine was added in a way so that the reaction temperaturedid not exceed 106° C. After the addition of the catalyst, the mixturewas stirred for another hour at 90° C. before the mixture was allowed tocool down to room temperature. Viscosity: 35000 mPas at 25° C. Molecularweight average Mw=6500, molecular number average Mn=3610.

Example 10

[0044] A mixture of 57.0 g of trimethylolpropane triacrylate, 37.0 g oftripropylene glycol diacrylate and 5.0 of 1-hydroxycyclohexyl phenylketone (Irgacure 184, Trademark of Ciba) was treated under stirring atroom temperature with 5.0 g of tri-n-octylphosphine, whereas thereaction temperature raised to approximately 40-50° C. The mixture wasallowed to cool down to room temperature. Viscosity: 200 mPas at 25° C.

Example 11

[0045] 10.0 g of trimethylolpropane triacrylate was treated with 0.05 gof tris(4-methoxyphenyl)phosphine. Under stirring the solid catalyststarted to dissolve and the temperature increased to approximately45-55° C. Then, the mixture was allowed to cool down to room temperatureand strirred for 24 hours at room temperature. Viscosity: 950 mPas at25° C. Molecular weight average Mw=1370, molecular number averageMn=980.

Example 12

[0046] 10.0 g of trimethylolpropane triacrylate was treated with 0.10 gof tris(4-methoxyphenyl)phosphine. Under stirring the solid catalyststarted to dissolve and the temperature increased to 60° C. Then, themixture was allowed to cool down to room temperature and strirred for 24hours at room temperature. Viscosity: 7200 mPas at 25° C. Molecularweight average Mw=3780, molecular number average Mn=1360.

Example 13

[0047] 10.0 g of trimethylolpropane triacrylate was treated with 0.10 gof dicyclohexylphenylphosphine. Under stirring the solid catalyststarted to dissolve and the temperature increased to 45° C. after 5minutes of stirring. Then, the mixture was allowed to cool down to roomtemperature, yielding a colorless solution having a viscosity of 3600mPas at 25° C. Molecular weight average Mw=1812, molecular numberaverage Mn=1115.

Example 14

[0048] 10.0 g of trimethylolpropane triacrylate was treated with 0.25 gof dicyclohexylphenylphosphine. Under stirring the solid catalyststarted to dissolve and the temperature increased to 60° C. after 5minutes of stirring. Then, the mixture was allowed to cool down to roomtemperature, yielding a colorless solution having a viscosity of 92000mPas at 25° C. Molecular weight average Mw=9182, molecular numberaverage Mn=3812.

Example 15

[0049] 50.0 g of pentaerithitol tetracrylate was treated with 1.5 g oftri-n-octylphosphine at room temperature. After 5 minutes of stirringthe temperature increased to 50° C. Then, the mixture was allowed tocool down to room temperature, yielding a colorless solution having aviscosity of 1200 mPas at 25° C. Molecular weight average Mw=1040,molecular number average Mn=910.

Example 16

[0050] 50.0 g of dipentaerithitol hexacrylate was sparged with air (0.21per minute), warmed to 50° C. and treated with 1.5 g oftri-n-octylphosphine. After 5 minutes of stirring the temperatureincreased to 62° C. Then, the mixture was allowed to cool down to roomtemperature, yielding a colorless solution having a viscosity of 13600mPas at 25° C. Molecular weight average Mw=1768, molecular numberaverage Mn=1450.

Example 17

[0051] 10.0 g of trimethylolpropane triacrylate treated with 0.20 g ofhexamethylene triaminophosphine dissolved in 2.0 g of trimethylolpropanetrimethacrylate. The mixture started to increase in temperature andexhibited after the reaction faded away a viscosity of 600 mPas at 25°C.

What is claimed is:
 1. A curable resin composition comprising a curableoligomer which has an acryloyl group and a substituted methacrylategroup represented by the following structure


2. A curable oligomer according to claim 1, wherein the oligomer has amolecular weight of 300-15000 and a viscosity of 200-100000 mPas at 25°C.
 3. A curable resin composition according to claim 1, wherein thecurable resin composition further contains an initiator.
 4. A curableresin composition according to claim 1, wherein the composition furthercontains an unsaturated polyester.
 5. A curable resin compositionaccording to claim 1, wherein the composition contains a compound havingan active hydrogen atom.
 6. A curable resin composition according toclaim 5, wherein the compound having an active hydrogen atom is aβ-dicarbonyl compound.
 7. A process for preparing a curable oligomerhaving an acryloyl group and a substituted methacrylate grouprepresented by the following structure,

comprising a reaction step of reacting at least one monomericmultifunctional acrylate in the presence of a tertiary organicphosphine.
 8. A process for preparing a curable oligomer according toclaim 7, wherein the monomeric multifunctional acrylate is a di-, tri-,tetra-, penta- or hexa-functional acrylate.
 9. A process for preparing acurable oligomer according to claim 7, wherein the monomericmultifunctional acrylate is used as a mixture thereof.
 10. A process forpreparing a curable oligomer according to any one of claims 7-9, whereinthe tertiary organic phosphine is added continuously to the monomericmultifunctional acrylate.
 11. A process for preparing a curable oligomeraccording to any one of claims 7-10, wherein the amount of addedtertiary organic phosphine is within the range of 0.1-25% by weightbased on the total weight of the reaction mixture.
 12. A process forpreparing a curable oligomer according to any one of claims 7-11,wherein the reaction temperature is within the range of 30 to 140° C.13. A process for preparing a curable oligomer according to any one ofclaims 7-12, wherein the multifunctional monomeric acrylate is selectedfrom the group consisting of 1,4-butandiol diacrylate, 1,6-hexandioldiacrylate, dipropylenglycol diacrylate, neopentylglycol diacrylate,ethoxylated neopentylglycol diacrylate, propoxylated neopentylglycoldiacrylate, tripropylene glycol diacrylate, bisphenol-A diacrylate,ethoxylated bisphenol-A diacrylate, poly(ethylene)glycol diacrylate,trimethylolpropane triacrylate, ethoxylated trimethylolpropanetriacrylate, propoxylated trimethylolpropane triacrylate, propoxylatedglycerol triacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate,pentaerythritol triacrylate, ethoxylated pentaerythritol triacrylate,pentaerythritol tetraacrylate, ethoxylated pentaerythritoltetraacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritolpentaacrylate and dipentaerythritol hexaacrylate.
 14. A process forpreparing a curable oligomer according to any one of claims 7-12,wherein the tertiary organic phosphine is selected from the groupconsisting of triethylphosphine, tripropylphosphin,triisopropylphosphine, tributylphosphine, triisobutylphosphine,tri-tertiary-butylphosphine, tris(2,4,4-trimethylpentyl) phosphine,tricyclopentylphosphine, tricyclohexylphosphine, tri-n-octylphosphine(TOP), tri-n-dodecylphosphine, trivinylphosphine, tribenzyl phosphine,dimethylphenylphosphine, cyclohexyldiphenylphosphine,dicyclohexylphenylphosphine, 1,2-bis(diphenylphosphino)ethane,1,3-bis(diphenylphosphino)propane, 1,4-bis(diphenylphosphino)butane,diphenyl(2-methoxphenyl)phosphine, tris(4-methoxyphenyl)phosphine,tris(2,6-dimethoxyphenyl)phosphine,tris(4-dimethylaminophenyl)phosphine, hexamethylenetriaminophosphine andhexaethylene triaminophosphine.